In methods of forming integrated circuits, it is frequently desired to electrically isolate components of the integrated circuits from one another with an insulative material. For example, conductive layers can be electrically isolated from one another by separating them with an insulative material. Also, devices which extend into a semiconductive substrate can be electrically isolated from one another by insulative materials formed within the substrate and between the components, such as, for example, trench isolation regions.
A suitable insulative material for isolating components of integrated circuits is silicon dioxide, which has a dielectric constant of about 4. In some applications, it is desired to utilize insulative materials having dielectric constants lower than that of silicon dioxide to reduce parasitic capacitance from occurring between conductive components separated by the insulative material.
A recently developed technique of forming silicon dioxide is a Flowfill.TM. technology, which has been developed by Trikon Technology of Bristol, U.K. In such process, SiH.sub.4 (in a gaseous form) and H.sub.2 0.sub.2 (in a liquid form) are separately introduced into a chamber, such as a parallel plate reaction chamber. A reaction between SiH.sub.4 and H.sub.2 O.sub.2 can be moderated by introduction of nitrogen into the reaction chamber. s A wafer is provided within the chamber, and ideally maintained at a suitably low temperature, such as 0.degree. C., at an exemplary pressure of 1 Torr to achieve formation of a silanol-type structure of the formula Si(OH)x, which is predominantly Si(OH).sub.4. The Si(OH).sub.4 condenses on the wafer surface. Although the reaction occurs in the gas phase, the deposited Si(OH).sub.4 is in the form of a viscous liquid which flows to fill small gaps on the wafer surface. In applications where deposition thickness increases, surface tension drives the deposited layer flat, thus forming a planarized layer over the substrate.
The liquid Si(OH).sub.4 is converted to a silicon dioxide structure by a two-step process occurring in two separate chambers from that in which the silanol-type structure was deposited. First, planarization of the liquid film is promoted by increasing the temperature to above 100.degree. C., while maintaining the pressure at about 1 Torr, to result in solidification and formation of a polymer layer. Thereafter, the temperature is raised to approximately 450.degree. C., while maintaining the pressure of about 1 Torr, to form SiO.sub.2. The processing at 450.degree. C. also provides an advantage of driving undesired water from the resultant SiO.sub.2 layer. Flowfill.TM. technology has also been utilized to form insulative materials comprising (CH.sub.3).sub.y SiO.sub.(2-y), wherein y/2 is the percentage of CH.sub.3 incorporated. Specifically, methylsilane is utilized in place of silane in the above-described reaction with hydrogen peroxide, and forms methylsilanol. The methylsilanol is a viscous liquid which flows over a substrate to fill gaps. Subsequently, the methylsilanol is treated with energy (such as heat) to drive water from the methylsilanol and form (CH.sub.3).sub.y SiO.sub.(2-y). The (CH.sub.3).sub.y SiO.sub.(2-y) has a dielectric constant of less than or equal to about 3, and is accordingly less likely to be involved in parasitic capacitance than is silicon dioxide. It would be desirable to develop alternative methods of forming insulative materials.